"Have faith" people quip. Faith in what? What meaning is there with the social saying, "have faith?" The Christian faith is no empty, vapid, heartfelt desire, it is a substantive faith.

Yet [Abraham] did not waver through unbelief regarding the promise of God, but was strengthened in his faith and gave glory to God, being fully persuaded that God had power to do what he had promised.
--Romans 4:20,21 TNIV

When Christians affirm that they are "saved by faith," it has little connection to the saying, "have faith." Saving faith, even having faith for the disciple of Jesus Christ is not a feeling in the heart, but a trust in the character, the person of God. Abraham's faith grounded itself in God's promises to him.

Paul writes to the Romans, and to us, announcing that the faith of Abraham was not wishful thinking, but a substantive reliance on who God is and on God's proven track record of forever faithfulness. "Have faith," indeed, but keep in mind, that faith is in the character, the reliability of the God we worship and serve.